Large slow-running two-stroke engine with sip lubricant injector

ABSTRACT

Disclosed is lubrication for a slow-running two-stroke engine, especially marine diesel engines. The lubrication uses Swirl Injection Principle by locating the lubricant injectors closer to the TDC than ⅕ of the full stroke of the piston, which is closer than in typical marine diesel engines. This can be achieved by reconstructing cylinder liners or by adding new mounting holes to the cylinder. In case that such reconstruction is not possible, an improvement of SIP principles can also be achieved by directing the spray towards the TDC or to a location on the cylinder liner closer to the TDC as compared to the location of the SIP valves, for example under an angle of more than 30 degrees or even more than 60 degrees when measured from a plane normal to the cylinder axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No.PCT/DK2015/050329 having a filing date of Oct. 28, 2015, the entirecontents of which is hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a large slow-running two-stroke engine, forexample marine diesel engine or gas or diesel engine in a power plant,with lubricant injector near the Top Dead Center (TDC) of the piston inthe cylinder.

BACKGROUND

Due to the focus of on environmental protection, efforts are ongoingwith respect reduction of emissions from marine engines. This alsoinvolves the steady optimization of lubrication systems for suchengines. Thereto is added increased competition and the economic aspectsof reducing oil consumption, as this is a significant part of theoperational costs of ships. A further concern is proper lubricationdespite reduced lubricant because the longevity of diesel engines shouldnot be compromised by the reduction of oil consumption. Thus, there is aneed for steady improvements with respect to lubrication.

For lubricating of large slow-running two-stroke marine diesel engines,several different systems exist, including injection of lubrication oildirectly onto the cylinder liner or injection of oil quills to thepiston surface.

An alternative method, commercially called Swirl Injection Principle(SIP), is relatively new and based on injection of a spray of atomizeddroplets of lubrication oil into the scavenging air swirl inside thecylinder. The helically upwards directed swirl results in the lubricantbeing pulled towards the Top Dead Centre (TDC) of the cylinder andpressed outwards against the cylinder wall as a thin and even layer.This is explained in detail in International Patent ApplicationWO2010/149162. The lubricant injectors are non-return valves thatcomprise an injector housing inside which a reciprocating valve memberis provided, typically a valve needle. The valve member, for examplewith a needle tip, in a valve housing closes and opens the lubricant'saccess to a nozzle aperture according to a precise timing. In currentSIP systems, a spray with atomized droplets is achieved at a pressure of35-40 bars, which is substantially higher that the oil pressure of lessthan 10 bars that are used for systems working with compact oil jetsthat are introduced into the cylinder. In some types of SIP valves, thehigh pressure of the lubrication oil is also used to move aspring-loaded valve member against the spring force away from the nozzleaperture such that the highly pressurised oil is released therefrom asatomized droplets. The ejection of oil leads to a lowering of thepressure of the oil inside the valve member, resulting in the valvemember returning to its origin until the next lubricant cycle wherehighly pressurized lubrication oil is supplied to the lubricant injectoragain.

In such large marine engines, a number of injectors are arranged in acircle around the cylinder in a plane perpendicular to a cylinder axisand each injector comprises one or more nozzle apertures at the tip fordelivering lubricant jets or sprays into the cylinder from eachinjector. Examples of SIP lubricant injector systems in marine enginesare disclosed in international patent applications WO02/35068,WO2004/038189, WO2005/124112, WO2010/149162, WO2012/126480,WO2012/126473, and WO2014/048438, which are herewith incorporated byreference.

Traditionally, the cylinders of engines have been built with openingsfor oil injectors placed at a distance from the top dead centre (TDC) ofthe cylinder, where the distance about ⅓ or more of the total stroke ofthe cylinder. However, for increasing length of the cylinders,considerations apply whether the lubrication nozzles should be movedfurther towards the TDC in order to safeguard a proper lubrication inthe cylinder near the TDC, where the heat is high and where therequirements for proper lubrication are most critical. For oil quillsthat are applied to the piston directly, such considerations have beendisclosed by Miyake et al. in the article “PAPER NO.: 177 Cylinder linerand piston ring lubrication issues in relation to increase stroke/boreratio”, published by the International Council on Combustion Engines atthe CIMAC Congress 2013 in Shanghai. In these experiments, it was foundthat the positioning of the lubrication valves at large distance of 1.2m from the TDC resulted in the oil not being scraped into the combustionchamber. From the perspective of oil refreshment and neutralization ofsulphuric acid in the combustion chamber, re-positioning of thelubrication valves closer to the TDC at 0.3 m was found advantageous, as67% of the oil would be scraped into the combustion chamber. However,for overall lubrication of the entire cylinder, two-level lubricationimproved the situation much with 20% of the oil scraped into thecombustion chamber.

As compared to scraping of oil quills into the upper part of thecylinder, special considerations apply for SIP lubrication because partof the spray from the SIP valve nozzles is drawn helically upwardstowards the TDC and into the combustion chamber and therefore provides abetter lubrication even over a large distance from the SIP nozzles tothe TDC. This is also why changing from quill scraping of oil to SIPlubrication has proven general improved conditions. For these reasonalso, it is generally not believed that a moving of the SIP injectors toa position closer to the TDC would yield any improvement that wouldjustify the modification of cylinder liners. Especially, an improvementas it was found by Miyake et al. for the re-positioning of the oil quilllubrication valves cannot be expected. Thus, although, one may speculatein moving the quill nozzles or the jet nozzles of more traditionallubrication systems further towards the TDC, these considerations do notappear to apply for lubricant sprays of SIP lubrication principles dueto the oil-transporting helical swirl.

However, despite these apparent advantages of SIP lubrication systems, ageneral steady motivation for improvements exists.

SUMMARY

An aspect relates to improving lubrication with SIP valves. It is afurther aspect to reduce wear on the cylinder in a large slow-runningtwo-stroke engine, especially in marine diesel engines. These aspectsare achieved by a system and method for improved lubrication in a largeslow-running two-stroke engine as described in detail in the following.

Although, the SIP lubrication principle, since its introduction, hasbeen recognised as improvements over oil quill lubrication, because thespray is swirled towards the TDC and lubricates the combustion chamber,an even further recent improvement for lubrication was achievedexperimentally in SIP lubrication by locating the SIP injectors closerto the TDC. Especially, much less wear than expected was foundexperimentally in the cylinder liner providing the SIP spray injectorsat a relative distance from the TDC of ⅛ instead of ⅓ of the full strokedistance of the piston. During mechanical run-in, also called break-in,of an engine after replacement of the cylinder liner, it was found thatthe wear in the new liner was not larger than the wear in a cylinderthat had been running for more than 1000 hours. This was utmostsurprising, as the wear in the run-in period of an engine after changeof a cylinder liner is very well known to be much larger than in theperiod following the running-in. Thus, despite the earlier generaladvantages and better performance of SIP lubrication as compared toother lubrication systems, a further improvement was possible.

Although, the experiments were performed with SIP injectors at arelative distance from the TDC of ⅛ of the full stroke, it is believedthat the distance for improved SIP lubrication can be extended to ⅙ oreven ⅕ of the full stroke, which is a position of the SIP injectorscloser to the TDC than in traditional engines, where it is typicallyaround ⅓ of the full stroke. Due to the fact that experiments take longtime, experimental evidence has not yet been provided for the effectalso being achieved at ⅙ and ⅕ relative distances, however, thoroughtechnical considerations and first qualitative indications appear tosupport this.

The re-positioning of the SIP injectors relatively to the TDC can beachieved by correspondingly constructing cylinder liners from the onsetwith mounting holes close to the TDC or by adding new mounting holes toexisting cylinder liners, where the new mounting holes are closer to theTDC than the original ones.

In those cases where reconstruction of a cylinder liner with injectormounting holes closer to the TDC is not possible, an improvement of SIPprinciples can also be achieved by changing the lubricant spraydirection from the typical 0-20 degrees to a larger angle towards theTDC, in order to direct the spray from the SIP injectors towards the TDCor to a location on the cylinder liner closer to the TDC as compared tothe location of the SIP valves, for example under an angle of more than30 degrees, more than 45 degrees or even more than 60 degrees whenmeasured from a plane normal to the cylinder axis.

The improvement by directing the spray towards the region close to theTDC is believed less efficient than the location of the spray injectorsin that region, however, it can be a useful alternative if the lubricantinjectors cannot be provided close enough to the TDC, for example due toconstructional constraints around the cylinder liner. For optimizationin some cases, the two described methods of positioning the injectorsclose to the TDC and the spraying towards the TDC can be combined, ifthis is found advantageous.

The term large slow-running two-stroke engine is meant for engines thathave a size that is typically used for ships and power plants, forexample with a cylinder diameter of more than 30 cm or even more than100 cm. Typical engines of concern are diesel engines, although also gasdriven engines can be used. Special use of the lubrication system andmethod is for large slow-running two-stroke diesel engine in ships.

Such an engine comprises a plurality of cylinders, each with a pistoninside, the piston reciprocating along a longitudinal cylinder axisbetween a top dead centre, TDC, and a bottom dead centre, BDC, thedistance between the TDC and the BDC corresponding to a full stroke. Thecylinder comprises a plurality of lubricant injectors distributed alonga perimeter of the cylinder, for example with identical angulardistance, between the TDC and the BDC for injection of lubricant intothe cylinder at various positions on the perimeter; wherein eachlubricant injector comprises a spray nozzle with an aperture forejecting a spray. Most lubricant injectors only have one aperture in thenozzle, although the spray nozzle may also be provided with multipleapertures. The direction of the spray is defined as an average directionof the droplets in the spray. In some embodiments, the atomised spray,also called mist, from a first nozzle is directed towards the cylinderliner into the region between the first nozzle and the next nozzle onthe perimeter.

The lubricant injectors are functionally connected to a control systemthat is configured for providing lubrication oil at a predeterminedlubricant pressure to the lubricant injectors through a correspondingpipe system and which is configured for controlling the timing ofinjection of lubricant into the cylinder. The timing, in turn, is linkedto the revolutions of the engine, for example with one injection perrevolution or one injection for each second revolution. The timing ofthe injection is determined by periodic increased pressure of the oilthat is supplied to the lubricant injectors. For example, the injectionis performed, once the oil pressure exceeds a certain predeterminedthreshold inside the lubricant injector.

For the SIP principle, each of the lubricant injectors is provided witha nozzle extending into the cylinder. The nozzle is dimensioned toprovide sprays with atomized droplets of lubrication oil, also calledmist of oil, when being provided with lubrication oil at thepredetermined threshold lubricant pressure.

The control system is also configured for causing the lubricantinjectors to inject the spray into scavenging air in the cylinder priorto the piston passing the lubricant injectors in its movement towardsthe TDC for diffusing the atomized droplets in the scavenging air anddistributing the atomized droplets onto the cylinder wall by transportof the atomized droplets in a direction towards the TDC utilising aswirling motion of the scavenging air towards the TDC.

In particular, the nozzles of the lubricant injectors in the cylinderare located at a first specific distance from the TDC, the firstspecific distance being less than or equal to a fraction of the fullstroke of the piston, the fraction being ⅕. For example, the firstspecific distance is less than ⅙, 1/7, or ⅛ of the full stroke.

In order to provide a proper SIP lubrication during running of theengine, sprays with atomized droplets of lubrication oil are repeatedlyinjected into scavenging air in the cylinder by the lubricant injectorsprior to the piston passing the lubricant injectors in its movementtowards the TDC. In the scavenging air, the atomized droplets arediffused and distributed onto the cylinder wall, as they are transportedin a direction towards the TDC due to a swirling motion of thescavenging air towards the TDC.

The atomization of the spray is due to highly pressurized lubricationoil in the lubricant injector at the nozzle. The pressure is higher than10 bars, typically between 25 bar and 100 bar for this high pressureinjection. An example is an interval of between 30 and 80 bars,optionally between 35 and 50 bars.

For example, the lubricant injectors comprise a spray nozzle havingaperture of between 0.1 and 1 mm, for example between 0.2 and 0.5 mm,for ejecting the spray or atomized droplets, also called mist of oil.

Also, the viscosity influences the atomization. Lubrication oils used inmarine engine, such as such as ExxonMobil® Mobilgard™ 560VS, have atypical kinematic viscosity of about 220 cSt at 40° C. and 20 cSt at100° C., which translates into a dynamic viscosity of between 202 and 37mPa·s. Other lubrication oils used for marine engines are otherMobilgard™ oils as well as Castrol® Cyltech oils, which have largely thesame viscosity in the range of 40-100° C. and are all useful foratomization, for example when having a nozzle aperture diameter of0.1-0.8 mm, and the lubrication oil has a pressure of 30-80 bars at theaperture and a temperature in the region of 30-100° C. or 40-100° C.

Typical for SIP lubrication is that the oil is not injected in a radialdirection, which is a direction from the cylinder liner towards thecentral cylinder axis. Instead, the nozzle aperture of the lubricantinjector is directed towards the cylinder wall at a spray direction thathas a tangential component that is larger than a radial component. Theradial component is parallel to a direction from the lubricant injectortowards the cylinder axis at the centre of the cylinder; and thetangential component is parallel to a direction tangential to thecylinder. For example, the atomised spray from a first nozzle isdirected towards the cylinder liner into the region between the firstnozzle and the next nozzle on the perimeter. Often, the nozzles arearranged with identical angular distance between the nozzle around thecylinder in a plane normal to the cylinder axis.

In order not to prevent the propagation of the spray from being hinderedin this direction by the material from the cylinder liner, the cylinderliner advantageously comprises a groove for each lubricant injector, thegroove extending from the nozzle aperture along the spray direction.

Although, new cylinder liners can be provided with mounting holes forlubricant injectors, where the mounting holes are provided at the firstspecific distance from the TDC from the onset, the system is also usefulfor retrofit of injectors, where additional mounting holes areestablished, for example by drilling the mounting holes through into thecylinder liner closer to the TDC than the original mounting holes.Optionally, the original mounting holes at a larger distance and theadditional holes closer to the TDC can both be used for mounting oflubricant injectors, although, often, the mounting holes at the largerdistance from the TDS would be blinded and not used for lubrication.

For example, the cylinder is provided with a first set of mounting holesfor lubricant injectors at a particular distance from the TDC, theparticular distance being more than ⅕ of the full stroke, for examplemore than ¼ or more than ⅓ of the full stroke. The cylinder is thenmodified by establishing a second set of mounting holes in the cylinderat a first specific distance from the TDC which is less than or equal toa ⅕ of the full stroke, for example less than or equal to ⅙ of the fullstroke or less than or equal to 1/7 or less than or equal to ⅛ of thefull stroke. Lubricant injectors are then mounted in the second set ofmounting holes, and using the second set of mounting holes for the sprayinjection. Typically, however, a distance closer than ⅛ of the fullstroke is not necessary.

In some practical embodiments, the lubricant injector comprises aninjector housing with a nozzle tip at one end of the injector housingfor reaching into the cylinder when the injector housing is mounted inthe cylinder wall. For example, the nozzle tip is an integral part ofthe injector housing, but this is not always the case. If the cylinderliner is provided with a groove for the spray, the nozzle tip reachesinto the groove. The nozzle tip comprises an aperture, extending from aninner cavity inside the injector housing and through a wall of thenozzle tip for ejection of pressurised lubrication oil from the innercavity and out of the injector housing through the aperture. Inside theinjector housing, there is mounted a valve member reciprocally slidingbetween an open and closed state of the injector. The valve member issealingly covering the aperture of the nozzle when in the closed statefor preventing access of lubrication oil to the aperture. The valvemember is moved away from the aperture of the nozzle during an openstate for giving access of the lubrication oil from the inner cavity tothe aperture during an oil ejection phase out of the aperture of thenozzle. The release of lubricant is stopped by subsequent decrease ofpressure in the chamber. The reciprocation of the valve member is donerepeatedly with a proper timing in accordance with the movement of thepiston.

For example, the lubricant injector receives lubrication oil from thecontrol system into the inner cavity of the lubricant injector at apredetermined pressure. The inner cavity is provided between the nozzleand the valve member such that moving of the valve member away from thenozzle aperture increases the volume of the inner chamber. Whenpressurised oil enters the inner chamber, it presses against the valvemember, for example against a shoulder of the valve member, forincreasing the volume of the inner chamber, and increased pressure abovea predetermined threshold pressure causes the valve member to bedisplaced from the nozzle aperture, giving way for release of thelubrication oil from the inner cavity through the aperture of thenozzle. In order to provide a high pressure inside the inner cavity,advantageously, the valve member is pre-stressed by a spring towards aposition where it covers and closes the aperture of the nozzle. For eachrepeated lubrication cycle, the lubrication oil is pumped into the innercavity at high pressure, for example at a pressure between 25 and 100bars, typically between 30 and 80 bars, and moves the valve member awayfrom the aperture. For example, the valve member has a shoulder againstwhich the pressurised lubrication oil is pressing in order to increasethe volume of the inner cavity and expel the lubrication oil out of thenozzle, once the pressure of the lubrication oil against the valvemember is larger than the pressure on the valve member by the spring. Inthis case, the spring pressure determines the threshold pressure forspray ejection

An example of an alternative method for moving the valve member is anelectromechanical system, for example a solenoid moving a magneticallyresponsive core or shell that is connected to the valve member. Thevalve member would then only be moved when the oil pressure issufficiently high for the aperture to provide the atomized spray.

Example for a spray injector in relation to the SIP principle isdescribed in the above-mentioned patent applications WO02/35068,WO2004/038189, WO2012/126480, WO2012/126473, and WO2014/048438. Alubrication control system is explained in detail in InternationalPatent Application WO2010/149162. These disclosures are herewithincorporated by reference.

In case that the cylinder liner cannot be provided with mounting holesfor injectors as close as the first specific distance, for examplebecause a cooling cap is preventing access for mounting or because thereare provided cooling channels inside the cylinder liner that would bebroken in a retrofit, a different method as mentioned above and asdescribed in more detail in the following can be used. This method isnot regarded as efficient as the provision of lubricant injectors closeto the TDC. However, relatively to the prior art, it would provideimproved lubrication. In coarse terms, the following method is a SIPlubrication method where the lubricant spray direction is changed fromthe typical 0-20 degrees to a larger angle towards the TDC, the anglebeing larger than 30 degrees, for example larger than 45 degrees or evenlarger than 60 degrees. The angle is measured from a plane normal to thecylinder axis. For example, this angle is in the range 30-80 degrees,optionally 45-80 degrees or 60-80 degrees.

By changing the spray direction towards the TDC, the lubrication oil iseasier transported towards the TDC by the swirl. In other words, theincreased inclination of the spray assists the swirl in thetransportation of the oil towards the TDC and into the combustionchamber.

Typically, when mounting the lubrication injectors close to the TDC,such highly inclined spray direction towards the TDC is not necessary.However, in principle, a higher inclined spray direction than 20 degreesmay be combined with the mounting of the lubricant injectors close tothe TDC as described above.

For example, the lubricant injectors are provided at a particulardistance from the TDC, the particular distance being more than ⅕ of thefull stroke of the piston, for example more than ¼ of the full stroke.In many engines, the lubricant injectors are provided at a distance fromthe TDC of around ⅓ of the full stroke or more. The lubricant injectorsare then mounted with a spray direction toward a region on the cylinderliner, the region being located between the TDC and a first specificdistance from the TDC, the first specific distance being less than ⅕ ofthe full stroke of the piston, for example less than or equal to ⅙, 1/7or ⅛ of the full stroke.

For example, the spray direction is directed towards the cylinder walland has a tangential component that is larger than a radial component,wherein the radial component is parallel to a direction from thelubricant injector towards a center axis of the cylinder and thetangential component is parallel to a direction tangential to thecylinder. In relation to the angle for the spray direction, the cylinderliner is potentially adjusted with corresponding grooves through whichthe spray can propagate largely unhindered from the nozzle of thelubricant injector into the cylinder in the spray direction.

The term spray is used herein as a term for an atomized ejection oflubricant, also termed mist of oil. The term lubricant is used forlubrication oil, different from diesel oil, especially due to its muchhigher viscosity, despite the diesel oil also having some degree oflubrication properties.

In order for the spray to not be directed radially into the cylinder bya first nozzle but rather quasi-tangentially, which means under a smallangle with the tangent, in order to spray oil on the cylinder linerbetween the first nozzle and the next nozzle on the perimeter, the lineris provided with grooves through which the spray can propagate into thecylinder on a quasi-tangential path. In the case, where the direction ofthe spray is directed towards the region near the TDC, it isadvantageous to provide grooves in the cylinder liner that unhinderedallows propagation of the spray in such direction. For example, thegroove is semispherical for allowing free adjustment of the spraydirection without hindering the propagation of the spray in the adjusteddirection.

The tangential component of the spray direction assists the swirl inaccelerating the oil mist in a helical movement towards the TDC.However, in principle, a radial injection is also possible with an angletowards the TDC as described above.

In summary, an improvement for lubrication is achieved in SIPlubrication by locating the SIP injectors closer to the TDC than afraction of the full stroke of the piston, where the fraction is lessthan ⅕, for example less than or equal to ⅛. This is closer to the TDCthan in traditional engines.

This can be achieved by reconstructing cylinder liners or by adding newmounting holes to the cylinder. In case that such reconstruction is notpossible, an improvement of SIP principles can also be achieved bydirecting the spray towards the TDC or towards a location closer to theTDC as compared to the location of the SIP valves, for example under anangle of more than 30 degrees, more than 45 degrees or more than 60degrees when measured from a plane normal to the cylinder axis. Also,the two described methods can be combined.

BRIEF DESCRIPTION

Some of the embodiments will be described in detail, with references tothe following Figures, wherein like designations denote like members,wherein:

FIG. 1a illustrates a top view of a cylinder lubrication system in alarge slow-running two-stroke engine, for example a marine dieselengine;

FIG. 1b illustrates a side view of a cylinder lubrication system in alarge slow-running two-stroke engine, for example marine diesel engine;

FIG. 1c illustrates a cylinder lubrication system in a largeslow-running two-stroke engine, for example marine diesel engine;

FIG. 2a shows a first type of an injector;

FIG. 2b shows a second type of an injector;

FIG. 2c shows a third type of an injector; and

FIG. 3 shows experimental data for an engine in which two cylinders wereamended to lubricant injectors closer to the TDC.

DETAILED DESCRIPTION

FIG. 1a illustrates one half of a cylinder of a large slow-runningtwo-stroke engine, for example marine diesel engine. The cylinder 1comprises a cylinder liner 2 on the inner side of the cylinder wall 3.Inside the cylinder wall 3, there are provided a plurality of lubricantinjectors 4 distributed along a circle with identical angular distancebetween adjacent injectors 4. The injectors 4 receive lubrication oilfrom a lubricator pump and controller system 11 through lubricationsupply lines 9. The supplied oil is typically heated to a specifictemperature, for example 50-60 degrees. Some of the lubricant isreturned to the pump by lubricant return lines 10. The lubricator pumpand controller system 11 supplies pressurised lubrication oil to theinjectors 4 in precisely timed pulses, synchronised with the pistonmotion in the cylinder 1 of the engine. For the synchronisation, thelubricator pump and controller system 11 comprises a computer thatmonitors parameters for the actual state and motion of the engine,including speed, load, and position of the crankshaft, as the latterreveals the position of the pistons in the cylinders.

Each of the injectors 4 has a nozzle 5 with an aperture from which anatomized spray 7 of lubrication oil, also called oil mist, is ejectedunder high pressure into the cylinder 1. For example, the nozzleaperture has a diameter of between 0.1 and 0.8 mm, such as between 0.2and 0.5 mm, which at a pressure of 10-100 bars, for example 25 to 100bars, or typically 30 to 80 bars, atomizes the lubricant into a finespray, which in in contrast to a compact jet of lubricant. The swirl 9of the scavenging air in the cylinder 1 presses the spray 8 against thecylinder liner 2 such that an even distribution of lubrication oil onthe cylinder liner 2 is achieved. This lubrication system is known inthe field as Swirl Injection Principle, SIP. Typically, the cylinderliner 2 is provided with grooves 6 for providing adequate space forpropagation of the spray from the injector in a non-radial way, asillustrated, where the direction is along the cylinder wall forlubricating the region between two adjacent nozzles, or even longer, asillustrated, assisting the transportation of the lubrication oil by theswirl.

In FIG. 1b , a schematic drawing is shown of a cylinder 2 inside which apiston 32 is reciprocating along a central cylinder axis 33 between abottom dead centre, BDC, and a top dead centre, TDC, the top dead centrebeing slightly below the cylinder top 35. The distance D of thelubricant injector from the TDC can be expressed in terms of length fromthe TDC or, alternatively, as is done herein in terms of fraction of thefull stroke, which is the distance between the TDC and the BDC.

FIG. 2a illustrates a first type 4 a of lubrication oil injector. Thegeneralized principle of the injector is similar to the ones disclosedin WO02/35068, WO2004/038189 or WO2005/124212 for a single nozzleaperture or as disclosed in WO2012/126480 for multiple nozzle apertures.These references also provide additional technical details as well asexplanations to the functioning of the injectors presented here, whichare not repeated here, for convenience.

The injector 4 a comprises an injector housing 12 having a nozzle tip 13which is integral with the injector housing 12 at one end. A nozzle 14with a nozzle aperture 14′ is provided in the nozzle tip 13 for ejectionof lubrication oil. The nozzle 14 also comprises a duct 20 that extendsfrom the nozzle aperture 14′ through the wall 21 of the nozzle tip 13into a cylindrical inner cavity 15 of the injector housing 12. A valvemember 16 is provided inside the injector housing 12. The valve member16 comprises a stem 17 that is slidingly guided for reciprocation insidea plain bearing 23, which in the shown embodiment is a separatestationary part inside the injector housing 12, although it could alsobe part of the injector housing 12, itself. As a coaxial longitudinalextension of the stem 17, a valve needle 18 is provided in the innercavity 15 of the injector housing 12. The valve needle 18 has a diameterthat is smaller than the diameter of the inner cavity 15 such thatlubrication can flow along the valve needle 18 and to the duct 20 andout of the nozzle aperture 14′ when a needle tip 22, for example aconical end part, at the end of the valve needle 18 is retracted from avalve seat 19 at a second end of the duct 14 such that the duct 20 isopen for flow of lubricant to the nozzle aperture 14′ from where it isejected. The position of the valve member 16 and the valve needle 18 ispre-stressed by the nozzle tip 13 by moderate spring pressure acting onthe opposite end of the valve member 16; and the valve member 16 withthe valve needle 18 is offset backwards away from the seat 19 byincrease of oil pressure in the cavity 15. The ejection of oil occurswhen the displacement of the valve member 16 by the oil pressureovercomes the pre-stressed force from the spring. In this way, thespring force regulates the pressure of the ejected oil. This isexplained in greater detail in the prior art references cited herein.

FIG. 2b illustrates a second type 4 b of lubrication oil injector. Thegeneralised principle of the injector is similar to the one disclosed inWO2014/048438. This reference also provides additional technical detailsas well as explanations to the functioning of the injector presentedhere, which are not repeated here, for convenience.

The injector 4 b comprises an injector housing 12 having a nozzle tip 13which is integral with the injector housing 12 at one end thereof. Anozzle aperture 14′ is provided in the nozzle tip 13 for ejection oflubrication oil. Inside a cavity 15 of the injector housing 12, a valvemember 16 is provided, the valve member 16 comprising a stem 17 and acylindrical sealing head 25 which is arranged slidingly in a cylindricalcavity part 15′ at the nozzle tip 13 of the injector housing 12. Theposition of the valve member 16 is pre-stressed backwards away from thenozzle tip 13 by a spring 26 and is offset forwards by oil pressureacting through a channel 28 upon the back part 27 of the stem, the oilpressure acting against the spring 26 force. The nozzle aperture 14′ issealingly covered by the sealing head 25 which abuts the cylindricalcavity part 15′ at the nozzle tip 13, unless the valve member 16 ispushed forward such that the sealing head 25 slides pass and away fromthe nozzle aperture 14′ to allow lubricant oil to flow from the innercavity 15 through the nozzle aperture 14′ for ejection.

FIG. 2c illustrates a third type 4 c of lubrication oil injector. Thegeneralised principle of the injector is similar to the one disclosed inWO2012/126473. This reference also provides additional technical detailsas well as explanations to the functioning of the injectors presentedhere, which are not repeated here, for convenience.

The injector 42 comprises an injector housing 12 having a nozzle tip 13,at which a nozzle 14 is provided with a duct 20 and a nozzle aperture14′ at a first end of the duct 20. The duct 20 extends from the nozzleaperture 14′ through the wall 21 of the nozzle tip 13 into the innercavity 15 of the injector housing 12. Inside the cavity 15 of theinjector housing 12, a valve member 16 is provided, the valve member 16comprising a stem 17 that is slidingly guided for reciprocation inside aplain bearing 23, which in the embodiment is shown as a separatestationary part inside the injector housing, although it could also bepart of the injector housing 12 itself. The position of the valve member16 is pre-stressed forward towards the nozzle tip 13 by a spring 26. Onepossible retraction mechanism is disclosed in WO2012/126473 in which anelectrical coil exerts an electromagnetic force on the valve member,which is equipped with a correspondingly electromagnetic responsivepart. However, in principle, it is also possible by suitableconstruction that the valve member 16 is offset backwards by increasedoil pressure in the cavity 15 acting on the valve member 16 against thespring 26 force. As a coaxial longitudinal extension of the stem 17, thevalve member 16 comprises a valve needle 18 to which there is fastened asealing ball member 28 as part of a needle tip 22, which in closed valveconditions is pressed against the seat valve 19 for closure of the duct20 and which in open valve conditions is offset from the seat 19 adistance to allow lubrication oil to pass from the inner cavity 15 passthe needle tip 22 with the ball 28 and into the duct 20 and out of thenozzle aperture 14′. By an O-ring 31, the inner cavity 15 is sealedbackwards towards the remaining parts inside the injector housing 12.

Typical dimensions for the injector housings are 10-30 mm in diameterand 50-130 mm in length, although, the injector including the back endwhere the supply lines are connected can be somewhat longer. The valvemember 16 has a typical length of 40-80 mm and a diameter of 5-7 mm atthe stem and a smaller diameter for the valve needle 18. The housing tip13 has a typical diameter of 6-10 mm, depending on the overall size ofthe injector housing 12. Nozzle apertures 14′ have a diameter within therange of 0.1 to 1 mm, for example within the range of 0.2 mm to 0.7 mm

FIG. 3 illustrates measurements on a marine diesel engine of the type9S90ME-C9.2-TII produced by MAN B&W®. The maximum liner wear wasmeasured for four cylinders. In a first cylinder, Cyl. 1, and a secondcylinder, Cyl. 2, the liner was changed after 1600 and 1800 hours ofrunning, respectively, to a new liner of a similar type, however, withmounting holes for the injectors provided at a distance from the TDC ofabout ⅛ of the full stroke, and a SIP injector connected to a HJLLubtronic™ system was installed. In a third cylinder, Cyl. 3, andfurther cylinder, Cyl. 4, after 1200 and 500 hours of running,respectively, with a traditional non-return valve, SIP injectors wereinstalled.

All SIP injectors were fed with lubrication oil from a HJL Lubtronic™system. The HJ Lubtronic™ system is an electronically controlled,hydraulic lubricator with load dependent lubrication for reducedcylinder oil consumption and optimised cylinder conditions, deliveringfresh cylinder oil with every piston stroke. The HJ Lubtronic™ system isbased on an electronically controlled cylinder lubricator at eachcylinder, which is operated electronically by a local controller,receiving information about synchronization of the system with theengine flywheel rotation and using engine load information as a controlparameter for the system. Control of each individual cylinder lubricatoris possible.

When comparing the curves in FIG. 3 before and after the change, it isseen from the graphs that the slopes different, which expressesdifferent speeds of wear. The speed of wear was respectively, around0.08 mm/1000 hrs for the non-return valves whereas it was around 0.03mm/1000 hrs for the SIP Lubtronic™® injection system.

As also seen in FIG. 3, the SIP valves at a distance of ⅛ and the SIPvalves at ⅓ show largely the same speed of wear. This is an utmostsurprising result because the wear during the first period of runningshould be much higher than for cylinder liners that are beyond therun-in period. The latter is common knowledge in the field and alsodescribed on page 5 in the document by MAN® called Service LetterSL2014-587/JAP. As the wear on new liners with the injectors at ⅛ strokeduring the run-in phase was much lower than expected, even lower thancould be expected with SIP injectors positioned from the TDC at ⅓ of thestroke, the use of a SIP system with spray injectors at a distance formTDC of ⅛ instead of ⅓ of the stroke can be interpreted as providing amuch better lubrication. The surprise stems from the fact that it wasgenerally believed in the field that the scavenging air wouldefficiently distribute the lubricant along the liner all the way up tothe TDC. However, these experimental results, as illustrated in FIG. 3proof differently in that a positioning of the lubricant injectors at adistance from the TDC of ⅛ instead of ⅓ yield a lower wear and thus,better lubrication near the TDC.

Although, the experiments have been performed with a distance from theTDC at ⅛ (0.125), of the full stroke, it is reasonable to believe thatthe effect is pronounced until a value of 1/7 or ⅙ or even ⅕ (=0.20) ofthe full stroke, whereas a surprisingly improved effect as compared tovarious earlier measurements with SIP injectors in marine diesel engineshas not been observed for a distance of ⅓ of the full stroke.

Although the present invention has been disclosed in the form ofpreferred embodiments and variations thereon, it will be understood thatnumerous additional modifications and variations could be made theretowithout departing from the scope of the invention.

For the sake of clarity, it is to be understood that the use of “a” or“an” throughout this application does not exclude a plurality, and“comprising” does not exclude other steps or elements. The mention of a“unit” or a “module” does not preclude the use of more than one unit ormodule.

The invention claimed is:
 1. A method for lubricating a largeslow-running two-stroke engine, the engine comprising a cylinder with apiston inside, the piston reciprocating along a longitudinal cylinderaxis between a top dead centre, TDC, and a bottom dead centre, BDC, thedistance between the TDC and the BDC corresponding to a full stroke; thecylinder being provided with a plurality of lubricant injectorsdistributed along a perimeter of the cylinder between the TDC and theBDC for injection of lubricant into the cylinder at various positions onthe perimeter; wherein the method comprises: providing the lubricantinjectors with only one spray nozzle having an aperture for ejecting aspray in a spray direction, which is an average direction of droplets inthe spray; during running of the engine, repeatedly injecting sprayswith atomized droplets of lubrication oil into scavenging air in thecylinder by the lubricant injectors prior to the piston passing thelubricant injectors in its movement towards the TDC, providing thelubrication oil to the lubricant injectors at a pressure of between 25bar and 100 bar for high pressure injection, and diffusing the atomizeddroplets in the scavenging air and distributing the atomized dropletsonto the cylinder wall by transporting the atomized droplets in adirection towards the TDC utilising a swirling motion of the scavengingair towards the TDC; providing the lubricant injectors in the cylinderat a first specific distance D from the TDC, wherein the first specificdistance is equal or less than ⅕ of the full stroke of the piston. 2.The method according to claim 1, wherein the first specific distance Dis equal or less than ⅙ of the full stroke of the piston.
 3. The methodaccording to claim 1, wherein the first specific distance D is equal orless than ⅛ of the full stroke of the piston.
 4. The method according toclaim 1, wherein the method comprises providing the lubricant injectorswith a spray nozzle having an aperture for ejecting the spray, theaperture having a diameter of between 0.1 and 0.8 mm.
 5. The methodaccording to claim 1, wherein the method comprises, providing a cylinderliner grooves through which the spray can propagate largely unhinderedfrom the nozzle of the lubricant injectors into the cylinder in thespray direction which is directed towards the cylinder wall and whereinthe spray direction has a tangential component that is larger than aradial component, wherein the radial component is parallel to adirection from the lubricant injectors towards a central axis of thecylinder and the tangential component is parallel to a directiontangential to the cylinder.
 6. The method according to claim 1, whereinthe method is a retrofit of lubricant injectors closer to the TDC andcomprises, providing the cylinder with a first set of mounting holes forlubricant injectors at a particular distance from the TDC, theparticular distance being more than a fraction of ⅕ of the full stroke,and modifying the cylinder by establishing a second set of mountingholes in the cylinder at a first specific distance D from the TDS whichis less than a fraction of ⅕ of the full stroke; mounting the lubricantinjectors in the second set of mounting holes, and using the second setof mounting holes for the spray injection.
 7. The method according toclaim 6, the method further comprising blinding the first set ofmounting holes and only using the second set of mounting holes for thelubricant injectors.
 8. A use of a method according to claim 1 forlubricating a large slow-running two-stroke marine diesel engine.
 9. Asystem for lubricating a large slow-running two-stroke engine, theengine comprising a cylinder with a piston inside, the pistonreciprocating along a longitudinal cylinder axis between a top deadcentre, TDC, and a bottom dead centre, BDC, the distance between the TDCand the BDC corresponding to a full stroke; the cylinder comprising aplurality of lubricant injectors distributed along a perimeter of thecylinder between the TDC and the BDC for injection of lubricant into thecylinder at various positions on the perimeter; wherein the lubricantinjectors comprise a spray nozzle having an aperture for ejecting aspray in a spray direction, which is an average direction of thedroplets in the spray; the lubricant injectors being functionallyconnected to a control system that is configured for providinglubrication oil at a predetermined lubricant pressure to the lubricantinjectors and configured for controlling the timing of injection oflubricant into the cylinder; the lubricant injectors being provided witha nozzle extending into the cylinder, the nozzle having a nozzleaperture dimensioned to provide sprays with atomized droplets oflubrication oil when being provided with lubrication oil at thepredetermined lubricant pressure where the predetermined oil pressure isbetween 25 bar and 100 bar; the control system being configured forcausing the lubricant injectors to inject the spray into scavenging airin the cylinder prior to the piston passing the lubricant injectors inits movement towards the TDC for diffusing the atomized droplets in thescavenging air and distributing the atomized droplets onto the cylinderwall by transport of the atomized droplets in a direction towards theTDC utilising a swirling motion of the scavenging air towards the TDC;wherein the nozzles of the lubricant injectors in the cylinder arelocated at a first specific distance D from the TDC, the first specificdistance being equal to or less than ⅕ of the full stroke of the piston.10. The system according to claim 9, wherein the first specific distanceD is equal or less than ⅙ of the full stroke of the piston.
 11. Thesystem according to claim 10, wherein the first specific distance D isequal or less than ⅛ of the full stroke of the piston.
 12. The systemaccording to claim 9, wherein the lubricant injectors comprise the spraynozzle having aperture of between 0.1 and 0.8 mm for ejecting the spray.13. The system according to claim 9, wherein the lubricant injectorscomprise the nozzle with an aperture that is directed towards thecylinder wall for providing a spray direction with a tangentialcomponent that is larger than a radial component, wherein the radialcomponent is parallel to a direction from the lubricant injector towardsthe central axis of the cylinder and the tangential component isparallel to a direction tangential to the cylinder, wherein a cylinderliner comprises a groove for each lubricant injector, the grooveextending from the nozzle aperture along the spray direction for thespray propagating largely unhindered from the nozzle aperture along thespray direction on a path that is directed towards the cylinder wall.14. The system according to claim 9, wherein the lubricant injectorcomprise an injector housing; the injector housing comprising a nozzletip at one end of the injector housing for reaching into the groove whenthe injector housing is mounted in the cylinder wall; wherein a spraynozzle with an aperture is provided in the nozzle tip, the aperture ofthe nozzle extending from an inner cavity inside the injector housingand through a wall of the nozzle tip for ejection of lubricant from theinner cavity out of the injector housing through the aperture of thenozzle; wherein a valve member is provided inside the injector housing,the valve member being mounted reciprocal between an open and closedstate of the injector; the valve member sealingly covering the apertureof the nozzle when in the closed state for preventing access oflubrication oil to the aperture, and the valve member being movable awayfrom the aperture during an open state for giving access of thelubrication oil from the inner cavity to the aperture of the nozzleduring an oil ejection phase out of the aperture.
 15. The systemaccording to claim 14, wherein the valve member is pre-stressed by aspring to cover the aperture the nozzle, wherein the lubricant injectorsare configured for receiving lubricant from the control system via apipe system into the inner cavity at a variable pressure for repeatedlymoving the valve member away from the aperture by correspondinglyrepeated increasing of the pressure of the lubrication oil in the innercavity and give way for release of the lubrication oil from the innercavity through the aperture of the nozzle.
 16. A large slow slow-runningtwo-stroke marine diesel engine with a system according to claim 9 forlubricating the engine.